Solve for $x$ : $3\sqrt{x} - 9 = 7\sqrt{x} + 4$
Answer: Subtract $3\sqrt{x}$ from both sides: $(3\sqrt{x} - 9) - 3\sqrt{x} = (7\sqrt{x} + 4) - 3\sqrt{x}$ $-9 = 4\sqrt{x} + 4$ Subtract $4$ from both sides: $-9 - 4 = (4\sqrt{x} + 4) - 4$ $-13 = 4\sqrt{x}$ Divide both sides by $4$ $\frac{-13}{4} = \frac{4\sqrt{x}}{4}$ Simplify. $-\dfrac{13}{4} = \sqrt{x}$ The principal root of a number cannot be negative. So, there is no solution.